In a company and the like having numbers of extension telephones, telephone transfer devices or operators are used for enabling employees outside the company to make a call to an individual extension telephone from an outside line telephone. In a case, for example, where a telephone transfer device is used, a company disposes the telephone transfer device in an extension telephone network and assigns a representative number to the telephone transfer device.
Upon arrival of an incoming call from the outside line telephone, the telephone transfer device accepts an extension telephone number to be transferred from a caller by using voice response and connects the call to the extension telephone number. With such a mechanism, by calling a representative telephone number to designate an extension telephone number, a person outside the company is allowed to be connected with the extension telephone. When an operator is used, the operator receives an incoming call to a representative telephone. Then, through talking with a caller, accept an extension telephone number to be transferred and connect the call. Furthermore, there is a case where a mechanism is provided for charging a call from an employee outside the company on the company by setting a representative telephone number to be an incoming call charged number.
System in which a telephone transfer device or an operator is disposed, however, has a problem that processing to be executed by a caller might be laborious in a company or the like which has a plurality of extension telephone networks each managing a representative number. There is a case, for example, where a company has a plurality of bases geographically apart from each other, for each of which an extension network is set up and connected by a dedicated line and each extension network has a representative number. In this case, for making a call from an outside line telephone to an extension telephone, a caller needs to select a representative number corresponding to an extension telephone number to be called and make a call. Therefore, for calling an extension number, the caller needs to call a representative number corresponding thereto. Such selective use of a representative number is laborious for the caller.
Literature 1 recites the system having a plurality of private branch exchanges in which numbers of extension telephone terminals are accommodated. In the system, in a case where an incoming call arrives at a certain private branch exchange from outside, when an extension telephone terminal as an arrival destination fails to be accommodated in the private branch exchange, a calling source is notified of a telephone number of a private branch exchange in which the arrival destination is accommodated and an extension number of the extension telephone terminal.
Literature 2 recites a private branch exchange having an incoming number table. In such a private branch exchange, when an incoming call arrives from outside, the call is put to the extension telephone terminal according to the contents set at the incoming number table.
Literature 1: Japanese Patent Laying-Open No. H3-104367 (page 5, FIG. 2)
Literature 2: Japanese Patent Laying Open-No. 2003-78934 (paragraphs 0019-0023, FIG. 3)
According to the systems recited in Literatures 1 and 2, however, in a system including a plurality of private branch exchanges each having a representative number, a caller is not allowed to connect its own telephone terminal to a desired extension telephone terminal by simple operation or the like. In the system recited in Literature 1, a caller needs to newly make a call to a notified representative telephone number. The system recited in Literature 2 enables connection to a desired extension telephone terminal when a private branch exchange is specified. When a plurality of private branch exchanges exist, however, connection to a desired extension telephone terminal accommodated in an arbitrary private branch exchange will be difficult unless some improvement is made.